This invention relates to a slot array antenna which is used mainly in a radar device.
In a radar device such as a radar for vessels, the slot array antenna comprising a waveguide in which the sharp horizontal surface directivity characteristic is gained relatively easily is employed abundantly.
FIG. 2 shows a sectional view of the so-called open type slot array antenna housing only an antenna unit in a waterproof box (a radome) as one example of a prior slot array antenna.
A slot waveguide (11) shown in FIG. 2 is provided with a plurality of alternately inclined slits (not shown in figures) which constitute an array in an E surface of the waveguide with standard measurement.
A waveguide holder (12b) grasps and fixes the slot waveguide (11), and forms an adjustment portion (10) to adjust to a space of a flare (12a) and to stabilize a level polarization mode.
A screen (13) for cross polarization suppression is to remove vertical polarization component causing inclination slots which are remained slightly, and is a vertical lattice enough narrow to a wavelength (see FIG. 7). In this embodiment, the screen (13) is formed by bending a metal plate with a plurality of slits and secured on the waveguide holder (12b) by screws or rivets. Besides, the screen itself may be omitted, or installed inside a box radiation portion.
In this embodiment, the slot waveguide (11) is held on the above radiation portion by means of the waveguide holder (12b) processed by bending a sheet metal, and further constituting the adjustment portion (10) and forming flare (12a) to limit directivity in a vertical surface.
Several flare stays (18) are to support an upper portion of the flare (12a) mainly, and may be omitted when the flare (12a) is strong, for instance, the flare (12a) has enough thickness.
Generally, in an open type slot array antenna the full length of which is long and whose horizontal beam width is narrow, an electric power is supplied from one end of the slot waveguide (11), and another end of the slot waveguide (11) is terminated non-reflectively in an adjustment termination (not shown in figures).
Accordingly, a feeder (16) comprising a corner vent, a coaxial waveguide-to-connector adapter or a waveguide flange (not shown in figures) as a feeder opening of a different member is provided, and a feed waveguide (14) connected to the feeder (16) is employed in transmission to an end portion thereof.
FIG. 10 shows one embodiment of the feeder employing the corner vent. In FIG. 10, the feeder (16) is attached on a reinforcement plate (15) and connected to the feed waveguide (14) by welding.
A standard measurement waveguide, which is employed as the feed waveguide (14), is supported by the reinforcement plate (15) from end to end, being connected to the slot waveguide (11) by bending an end portion of it or by using a vent for an end fold (not shown in figures).
The reinforcement plate (15) is arranged over approximately the whole length in a longitudinal direction of the antenna, and secured by screws to the radome (19) and a pedestal (6) for attaching to a scanner main body near a center thereof.
When a part other than a radiation surface (19a) of the waterproof box is made of metal, the reinforcement plate (15) may be omitted.
A lower portion of the flare (12a) is connected with the reinforcement plate (15) by screws or rivets, and the reinforcement plate (15) is connected with a fastened portion of the slot waveguide holder (12b) and the reinforcement plate by screws or rivets respectively to hold a weight in the antenna and to reinforce an inner portion of the box. Besides, in his example, when the radiation surface (19a) and the box (19b) are formed of resin as a united radome, the radome itself can not be used for reinforcement because of time deterioration by ultraviolet rays, etc., generally. Furthermore, in the case of the so-called dome type small radar which houses a short small antenna and a transmitter-receiver in the waterproof box (not shown in figures), simplification takes precedence because a horizontal beam width is wide, so that a direct feeding from a center in a longitudinal direction of the slot waveguide is carried out.
In this case, there are many things to omit the feed waveguide, the reinforcement plate, the pedestal, etc., generally, to attach a coaxial rotation shaft directly at a center of the waveguide holder (12b) or the slot waveguide (11), and to feed after carrying out coaxial waveguide convert inside the center of the slot waveguide are many.
However, in the slot array antenna constituted thus, a gap is created partially in a contact surface (20) between the slot waveguide (11) and the waveguide holder (12b), so that the adjustment portion (10) does not function, and as a result, there is a possibility of disorder to the directivity.
Though it is necessary to make a plate thickness of the waveguide holder (12b) thicker and to increase fixing points between the screen (13) for removing the cross polarization and the waveguide holder (12b) and to press the contact surface (20) evenly, they disturb saving weight and simplifying assembly.
Because some parts relative to the reinforcement can not be reduced any more, new ideas are required for weight saving and simplification.